In some electric devices, such as circuit breakers, insulated switchgears, power distribution transformers, instrument transformers, surge arresters, cable terminations, pole heads, bushings, insulators and similar, there may be provided one or more volumes, or chambers filled with oil or an electrically insulating gas as an electrically insulating means. Oil has the advantage of being an efficient electric insulator and also being able of transmitting heat from heat-developing elements, such as the voltage-carrying elements in such devices. Since the oil is present in a liquid state, it has the advantage of being able to transmit heat by means of convection. However, the use of a liquid insulation such as oil may cause problems of leakage, and, as a consequence thereof, operation disturbances or even serious breakdowns. From an environmental point of view, oil is also undesirable.
Also when using insulating gases, such as SF6, as an insulating medium, there might be leakages that, in their turn, might result in operation disturbances or even breakdowns of equipment important for the transmission of current in medium and high voltage systems.
Accordingly, in order to remedy the drawbacks of prior art, recent search is focused on the development of dry insulations in which the oil, or gas, is substituted by a solid insulation element. Such solid insulation elements may comprise polymers such as polyurethanes or silicone-based polymers and may be present as a foam, a gel or even a rubber, depending on the specific application. The polymer should be possible to cast in the chamber or volume in which it is to be housed upon operation, in order to be able to continuously be in contact with or adhere to surrounding elements while leaving no pockets of air or other gas between itself and any such further element. However, a drawback of many polymers used for the forming of such insulation elements is their relatively low thermal conductivity, especially taken in combination with the fact that such solid insulation elements, unlike a liquid like oil, will be unable of transmitting heat through convection.
It is an object of the present invention to present an electric insulation device as initially defined, which presents an improved thermal conductivity compared to corresponding solutions of prior art.